1. Field
The present disclosure relates to a light driving apparatus and a method thereof, and more particularly, to a light driving apparatus and a method thereof adopting a Primary Side Regulation (PSR) manner which allows an Light Emitting Diode (LED) to operate effectively.
2. Description of the Related Art
As the LED technology has recently developed in various aspects such as light emission efficiency, high brightness, environment-friendly, low power consumption, and miniaturization, LED lights are spotlighted in the light source field.
In an LED light, a power source characteristic is one of main factors which determine the overall performance. The optical power of an LED varies according to the change of a power source, and so the stability of the power source is very important in order to maintain the optical power consistently. In addition, due to the nature of the LED light which should be controlled consistently, a constant current control method is preferred in the driving circuit of the LED light.
A general LED driving circuit according to the prior art uses a fly-back converter.
The fly-back converter is a known technique for detecting an error of an output voltage by providing an error sensing circuit to a secondary side output terminal, and feeding back the detected error value to a power converting circuit at a primary side through an opto coupler provided at the secondary side in order to stabilize the output voltage.
The fly-back converter demands a complicated circuit structure in order to protect against overvoltage during the constant-current control and the feedback open operation. In particular, since the secondary side needs a control circuit for constant current and constant voltage and many peripheral elements (including passive elements) such as an expensive opto coupler, the circuit structure for driving the LED light is complicated along with drawbacks such as high cost and difficult miniaturization.
FIG. 1 shows a Primary Side Regulation (PSR) driving circuit which simplifies the circuit design by reducing the number of parts of the secondary side to solve the above drawbacks.
The light driving apparatus of FIG. 1 is classified into a primary side and a secondary side based on a transforming circuit 30. The primary side includes circuit elements such as an AC power source 10, a rectifying circuit 20, a switching element 40, a control circuit 60, and an inductor 50, and the secondary side includes a LED unit 70, and a diode D1 and a capacitor C2 for rectifying and smoothing the voltage of the secondary side.
In the primary side regulation method as shown in FIG. 1, the primary side implements the constant-current control by using the feedback information of the secondary side, and accordingly many circuit elements of the secondary side may be removed (excluded). Therefore, the circuit structure may be simplified in comparison to the fly-back converter.
The rectifying circuit 20 rectifies AC power Vac output from the AC power source 10 into DC. The transforming circuit 30 transforms the magnitude of the primary side voltage output from the rectifying circuit 20 and outputs it to the secondary side. The secondary side output is rectified by a diode D1, charged in a capacitor C2, and then supplied in the form of DC power VOUT to the LED unit 70 which is a load.
The inductor 50 of the primary side is an auxiliary coil for the feedback of the secondary side current.
The control circuit 60 resistance-distributes voltage Vdd, which is drawn from the inductor 50 and charged in the capacitor C3 through the diode D2, to compare it with a reference voltage, and controls the switching element 40 accordingly to the comparison result to increase or decrease the amount of energy output to the LED unit 70, so that the voltage charged in the capacitor C2 of the output terminal is maintained consistently.
The control circuit 60 detects current Id flowing at the secondary coil of the transforming circuit 30 through the inductor 50 which is an auxiliary coil and uses the current for the constant-current control.
As described above, if the auxiliary coil of the primary side detects a value of the secondary side current and uses the value as secondary side feedback information for the constant-current control, an error or mistake may occur during a current detecting process. Therefore, the constant-current control function may not be easily implemented precisely.
In addition, the value of the secondary side current used as the feedback information by the control circuit 60 of the aforementioned primary side regulation type corresponds to a peak current. In case of the fly-back converter, the peak current is also generally used to implement constant current and constant voltage. However, since the peak current is a dynamic value which changes instantly, the use of a peak current deteriorates stability which is one of most important factors for LED operation even though the driving speed increases.